Many techniques used in the fabrication of electronic integrated circuit chips lend themselves readily to micromachining mechanical devices from semiconductor substrates. U.S. Pat. No. 5,058,856 to Gordon et al. describes a thermally actuated microminiature valve having a seat substrate that is fabricated using a first semiconductor wafer. The seat substrate includes a flow via and a raised valve seat structure that surrounds the flow via at a front surface. A second semiconductor wafer is patterned to include a central armature for alignment with the raised valve seat structure and to further include an array of legs extending from the central armature. Each leg has two metallic layers, with each of the two metals having substantially different coefficients of thermal expansion. As the legs are heated, the difference in thermal expansions of the two metallic layers causes the legs to arch, thereby displacing the central armature relative to the flow via. The Gordon et al. patent is assigned to the assignee of the present application and is incorporated herein by reference.
Micromachined valves are becoming increasingly common. U.S. Pat. Nos. 4,581,624 to O'Connor and 5,069,419 to Jerman also teach microminiature valves. While these patents do not include the array of legs described in the Gordon et al. patent, a common feature is an axially movable armature that includes a smooth silicon surface known as a valve face. The valve face opens and closes against a valve seat structure surrounding a flow via.
Within the above-cited prior art patents, fabrication practicalities play a major role in determining the design of the microminiature valve. Because of the uncertainties in etch rates within semiconductor fabrication, manufacturing tolerances are imposed upon the design of valve features. Overetching and underetching during creation of microminiature features must be considered. Another fabrication concern is that of misalignment, particularly in etching the flow via through the seat substrate of the valve.
It is an object of the present invention to provide a microminiature valve and a method of fabricating such a valve, wherein the pneumatic characteristics and thermal characteristics are improved without rendering the valves susceptible to a low manufacturing yield.